In this prospective intervention, the investigators studied Abolfazle outpatients who were referred to us by Bushehr University of Medical Sciences in Iran between January 1, 2008 and December 30, 2010. The study was approved by the institutional Ethics Committee of Bushehr University of Medical Sciences and all patients were required to provide written informed consent before the study commenced.There were 3 steps in which the investigators prescribed letrozole (Femara,Novartis,Quebec,Canada). In all cases, daily administration began on the 3rd day of the menstrual cycle through to the 7th day (totaling 5 days). In the first step the investigators prescribed letrozole at a dose of 2.5 mg (one tablet) for one or two cycles according to the patient's response. Normal follicular size and endometrial thickness were considered 18-24 mm and 6 mm or more respectively.1 If the follicle was deemed not acceptable, the dose of letrozole was increased at the next cycle.